Producing rod-shaped semiconductor crystals



PRODUCING ROD-SHAPED SEMICONDUCTOR CRYSTALS Filed Dec. 5. 1360 llll;

ceiving the separated semiconductor material.

v Y 3,232,745 PRODUCING ROD-SHAPED SEMICONDUCTOR CRYSTALS Theodor Rummel, Munich, Heinrich Kniepkamp, Karlsf ruhe, and iReiner': Emeis, lretzfeld,v Upper Franconia,

Germany, assignors to Siemens-8i Halske Aktiengesellschaft, Berlin and Munich, Germany, a German corporation v Filed Dec. 5, 1960,'Ser. No. 73,8019

7 Claims. (Cl. 75-10) This invention is concerned with producing rod-shaped l semiconductor crystals from a gaseous phase containing tion, in an electric gas discharge, of a gaseous compound which contains they corresponding semiconductor substance and which is intcrmixed preferably with purified hydrogen gas as a reducing agent, the material being deposited or precipitated on the electrodes provided for the gas dischcrge'and caused t-o'crystallize thereon.

It has also been proposed to employ the above indicated prior method for producing semiconductor rods. An electric arc discharge is for this purpose effected in a reaction gas containing the desired semiconductor substance, such discharge causing separation of the elementary semiconductor substance from the reaction gas. Underneath the area of the arc discharge is disposed a carrier or seedcrystal made of the corresponding semiconductor substance in the shape of a short crystal, which catches the finely distributed semiconductor material produced by the gas discharge. The upper end of the carrier crystal is thereby melted-` .the hot molten part preferentially re- The carrier crystal is gradually/ drawn downwardly, away from the area of the arc discharge. The lower part of the molten nrert'on which the separated material is precipitated is .thus cooled, causing continuous crystallization thereof and thereby effecting gradual growth of the rod-shaped semiconductor body. The speed of downward withdrawal of the growing rod-shaped semiconductor body is adjusted to the rate o? separation of the material from the gaseous phase, so thatt'ne size of the molten area and its'position with respect to the gas discharge zone remain as constant as possible. A

Instead otutilizing a gas discharge, purely thermal decomposition or reaction may be employed for separating the semiconductor material on a seed crystal made of the same material. Localization of the separation is in such case likewise possible, provided that only part of the surface of the carrier seed is caused to melt, since the formation of the liberated semiconductor material starts and is primarily effected at the hottest portions of the carrier. In accordance with a prior method, a rodsource which produces the melt, the melt thereby substantially retaining its relative heat source.

The prior methods provide for the separation of semiposition with respect to the 'Y y United States Pater ice material for progressive cooling or solidication-on the solid crystal carrier. The advantage of arranging the moltenarea at the upper end of the seed crystal resides n in'theffact that the melt rests upon a solid support which secures it in relativelyhigh degree against dropping ol. However, the interface between the-melt and the solid crystal body extends as a rule not along a plane area but is upwardly arched, since the cooling is primarily effected by heat conduction over the solid crystal body while the heating is effected by radiation from the outside. When it is intended to work instead of with a thin molten skin, with a relatively substantial amount of molten material, which is desirable in the interest of improved crystallization, there will appear the drawback that the melt is poorly localized in its position with respect to the crystal rod, such melt constantly assuming a changed position at the tip of the seed crystal. The reason for this situation is thatl the melt is in the known methods relatively well secured against dropping off, but the position thereof with respect to the. solid crystal carrier corresponds to a maximum of potential energyor at best to a condition of indifferent equilibrium. The disadvantage resides in the fact that the positionof the melt is changed even respont sive to slight disturbances, for example, such as are caused by gas ow or by the motion imparted to the crystal carrier, resulting necessarily in irregular diameter of the drawn body. The rodlike bodies are accordingly if irreg-y ular diameter and poor crystal quality, resulting in the further processing thereof to produce semiconductor devices, in great waste of costly semiconductor material.

The present invention recognizes that the above indicated disadvantages can be avoided in relatively simple manner by arranging the melt, on which the semiconductor substance is to be precipitated from the gas phase,

not at the upper end but at the lower end of the carrier which is made of the same material.

The present invention is accordingly concerned with a method of producing rod-shaped semiconductor crystals, comprising causing a reaction gas which contains the respective semiconductor substance or components thereof to interact with a melt carried by a solid crystal body made of the corresponding semiconductor substance, said melt receiving the substances liberated from the reaction gas by decomposition and forming the desired semiconductor material, and thereby effecting continuous growth of the solid crystal by crystallizing the substance precipitated thereon. In accordance with the invention, the

melt which is to be utilized is produced by melting the crystal body at the lower end thereof, such melt depending from the crystal body in the fashion of a drop on which liberated material is precipitated by the action of an energy source, the ,crystal body being withdrawn up-` wardly at a speed adjusted to the rate at which mate- `rial isv precipitated, thereby withdrawing the solid crystal shaped semiconductor crystal is melted at its upper end, y

body from the range of action of the energy source while maintaining the size of the melt substantially constant. The advantages which will be presently described more in detail and which have to do with utilizing a melt in v the form of a downwardly depending drop, will be secured by the provision of means for additionally supporting such melt drop. The support can be effected, for example, pneumatically or by the action of an electromagnetic eld, and in the latter case, if there is provided an electromagnetic energy source, by the action of such source. The molten drop may also be supported, without foregoing the advantages owing therefrom, by means of a crystal body disposed therebelow, the molten drop 3,232,745- Patented Feb. 1,

resting thereby inthe form of a -molten zone extending v'between the two vertically coextensive solid crystal bodies.

.A downwardly .depending molten drop would at iirst appear to be a relatively unstable structure which would 4be easily excited to execute resonance oscillations favoring dropping off, and would be in this respect inferior toa 'melt disposed at the upper end of the carrier; however, the tdownwardly depending' moltendr'op has the` for producing mono crystals than the prior method, when Y it is consideredthat the use of a melt depending downconsiderable advantage that it always assumes the lowerv most position lon lthe seed crystal. This is dueto the fact Accordingly, the position of since the melt, after decay of a disturbance, will automatically assunte its lowermost position at the seed crystal. When the size of the molten drop is held constant, by adjustment of the speed of crystallization to the speed of semiconductor precipitation or separation from the reaction gas, which is easily effected, the size of the interface surface with the solid seed crystal will llikewise remainv constant in the course of operation.

I The use of a downwardly depending drop-shaped melt at vthe lower end of the seed crystal must therefore necessarily .result in uniform rods 'growing in straight manner. v lvenuponusing at the start ofthe operation an irregularl' shapedfseed-crystal as a carrier, thecross-section ofthe p'rpduced-will quickly stabilize to a constant value, 'since the downwardly depending moltendrop which is held at a constant volume leads necessarily to uniformity of a crystallization front which might have been irregular at the start -of the process.

The precipitation or separation of the semiconductor substance at the hottest point in the reaction vessel, which is represented by'the downwardly depending molten drop,

bis at any rate secured, since the surface of the hot melt position,` while affording greater security against dropping off, will correspond to a maximum of the potential energy and therewith to an unstable equilibrium condition. While a case in which the adhesion is opposed to -the'force of gravity can never occur, whereby the acute danger of dropping off is' largely avoided, the position of the melt on the seed crystal is nevertheless by no means invariable, as already explained before, but depends to a high degree upon chance. The size and position of the.

recrystallization front is accordingly subjected to considerably greater fluctuations than in the case of a downwardly depending drop, and the production of uniformly grown .rods is consequently extraordinarily diflicult in connection with the previously known methods,

As an additional disadvantage of the prior method may be mentioned the fact that it is very difficult to produce with the use thereof mono crystal rods'. It must be considered'in this connection that thesize'of themelt and` therewith its temperature cannot be maintained .as desired above the melting point of the corresponding semiconductor and, accordingly, it may easily happen that islands of solidified semiconductor material are formed von the surface of the melt due to cooling.V

tion plane. These vislands have as is known the tendency to sink downwardly and they can thus directly reach the crystallization plane and be built thereinto if such plane is at the deepest point of the melt. The building-in of these islands into the crystallization plane usually results in a polycrystalline degeneration of a previously present n monocrystalline growth'. lIt will be realized that the meth- This possibility is' above all present in the neighborhood of the crystalliza-v od proposed by the present invention is considerably better wardly from ythe crystal body in the form of a drop forms a crystallization. plane which is on top while the -cryfstallization plane in the case o'f a-melt provided at the upper end of a crystal body is situated at the bottom.

The foregoing and further objects and features of the I invention will appear in the course of the description which is rendered below with reference to the accom` -tion thereof. A simple way of satisfying this requirement resides in supporting the melt pneumatically lby employing for this function the stream of reaction gas llowing into the apparatus. This can be effected as shown in FIG. l, by blowing the reaction gas discharged from a nozzle against the downwardly depending molten drop so as to support it. The same function can of course be fulfilled by an inert protective gas.

Another possibility of increasing the stability of the melt resides in supporting the corresponding molten drop by means of the action of an electromagnetic field.` As is known, an electromagnetic field can induce eddy currents in a conductive or in alsemiconductive material, such eddy currents imparting to the material a magnetic moment. However, to a body having a magnetic moment is imparted a force, in a non-homogeneous or an electromagnetic field, which endeavors to pull the body either vinto a region of higher field strength or to crowd it from the region of higher field strength. The induced magnetic moment is, in the case of a non-homogeneous field, in accordance with the known rule supplied by Lenz, so oriented that it attempts to crowd the body out of the region of higher field strength. When the electromagnetic iielrl affecting thebody increases in the direction of the force of gravity, the field will tend to move the body in opposite direction. The force of the eld with respect to the solid or uid body depends upon the amount of the magnetic moment induced in the body and upon the magnitude of the gradient of the electromagnetic field. It can accordingly be made very great by an appropriately high eld gradient inthe direction of the force of gravity as well as hy a suflciently high amplitude and/or frequency of the alternating field. The levitation, imparted to a conductive body in such field,- stops as soon as the body assumes a position in the held in which the force thereof balances the weight of the body. i

Such a iield is supplied by a short coil which is traversed by -alternating current, the axis of the coil coinciding with the axis of the crystal carrier rod, with the molten drop situated somewhat above the symmetry plane of the coil, in some situation even somewhat above the upper margin ofv the coil, the coil field being in such a case oriented radially symmetrical to the axis of the carrier and the molten drop adhering to the lower end thereof, and moreover diver-ging upwardly at any point of the molten drop. It follows, therefore, that an upwardly rlirected and at the same time inwardly oriented supporting force will beoperative with respect to all parts of the melt adhering in drop shape to the carrier. The dimensioning of the field strength as well as of the held gradient are a matter of experience and therefore must be determine-:l experimentally. depending especially upon the size of the molten drop. The endeavor should be to place the meridian lines of the drop so that they form with peripheral lines of the crystallized rod an approximately obtuse angle at the border between the solid and the uid phase. The

condition is still more favorable, in individual cases, for

These crystal bodies are drawn apart at a speed corresponding tothe rate of growth of material at the melt, thus withdrawing them from the range of action of the energy source which produces the melt. The operation canbe effected by using the arrangement shown in FIG. 2.

The advantages obtained `from a downwardly depending molten drop are, upon use of the second crystal body for supporting it, preserved at least lwith respect to the portion of -the rod extending upwardly from the melt. Moreover, as compared with a melt produced at vthe upper end of a seed crystal, 'the position of the contacting plane with the lower c rystal body is considerably stabilized. This particular embodiment of the invention permits especially quick execution of the operation, involving drawing apart of the two crystal bodies according to the rate at which material is separated at the melt, since crystallization is effected at the upper as well as at the lower crystal bodies. The molten zone can be advantageously produced by melting a portion 'of a vertically extending rodlike semiconductor crystal body along a, zone of limited length.

' Various known means can be additionally employed in realizing the present invention. Thus, axial rotation of the rod or of the parts of the rod which carry the moltenl zone, will benefit the uniformity of the heating of the melt,` thereby improving the properties of thev crystal to be produced. In the case of round rods, the melt can be maining of the crystal body upon start of the induction 7 operation.

The choice ofreaction gas to beemployed will depend j upon the kind of semiconductor rod which is to be produced. In the case of silicon rods to be produced, the

. materials to be considered aside from SiCl4, include higher tained in rotation by the use of an electric rotary field.

The material of the melt is for this purpose permeated by a magnetic field which is produced, for example, by two magnet poles which are oppositely disposed alongside the melt but out of engagement therewith. The magnet field will become a rotary field responsive to rotation of the magnet poles about the axis of the melt, such magnet field inducing a current into the molten material. The rulef supplied by Lenz, as a direct consequence of Faradays induction law, requires, that the inductionaction, effected in the molten material bythe rotation of the magnetic field, is subjected to local alteration, whereby the material of the melt is brought vinto a condition of rotation in the direction of rotation of the magnetic field. Another andeasier possibility for producing the rotating field resides in utilizing a three-phase current. Such current is conducted to a coil system, in a manner known from threephase motors, the melt functioning as the rotor. The coils are so oriented with respect to the melt, that the magnetic lines of force permeate the melt in a direction extending perpendicular to the axis thereof, that is, hori- Vtioned, this results in the advantage of simultaneously effecting an electromagnetic support for the melt by the action of the field of the induction coil, as soon as the melt is positioned above the median plane of the coil, such position vbeing automatically assumed by the upward withdrawal of the solid crystal body, away from the range of heating. The seed crystal is in the case of highly pure semiconductor material usually extremely high ohmic, and it will therefore be of advantage to provide for a preheatsilicon halides such as siliconhexachloride or siliconoctochloride as well as halogenated silanes such as siliconchloroform or corresponding higher homologs. In the case of germanium rods to be produced, there will be emv ploy'ed corresponding or appropriate germanium compounds. In order to facilitate separation of the semiconductor substance, hydrogen may be intermixed with the reaction gas, the hydrogen acting as a reducing agent. i

In the method according to the invention, the separation of the silicon or other semiconductor material is effected predominantly on the surface of the melt. In addition thereto, and especially when using silane, there may occur spurious silicon production in the free gas space, which may be effected in some situation by the temperature field of the melt, although such spurious separation would be very much less as compared with the separation at the melt` In order to assure that silicon which is' thus spuriously produced will reach the melt, gas streams, especially streams of the reaction gas may be directed against the melt or electrical means may be employed for this purpose. It is proposed to use for this purpose above all the so-called electric blast, an electric stream in the reaction space, which is produced, for example, by means of points. or knife edges disposed opposite the melt which is ing such body loses in the presence of high field strength its insulation property, due to ionization, thus becoming conductive, a discharge will occur at such edges or points. This discharge imparts to the atoms or molecules of the gas a mechanical motion directed away from the points or edges, such motion being referred to as electric blast. In the present case, there are provided two or more electrodes made of a metal, for example, tungsten, which is difficult to melt, such electrodes being provided with points extending in the direction of the melt and the crystal body carrying it, and a direct voltage of a few thousand volts is applied thereto, such voltage being however too low to effect a visible gas discharge. An electric blast will thus be produced in the reaction gas, which is directed toward thev melt, thereby blowing the semiconductor material separated in the free gas space thereagainst.

In the arrangement for realizing the invention, as illustrated in FIG. 1, the seed crystal 3 is, for example, a rodshaped highly pure silicon body which is disposed vertically in a quartz tube l, to the lower end of which is fused a tubular nozzle 2, such nozzle serving as an inlet for the reaction gas, for example, SiCla and H2. An induction coil 5 supplied with high frequency current from the source 7, which surrounds the lower end of the seed crystal rod 3, serves for producing the molten drop 4 at the lower end thereof. The arrangement of the gas inlet 2 underneath the molten drop 4, with the gas blowing thereagainst provides a pneumatic support for the drop and supply thereto of fresh reaction gas for direct contact with the melt, the gas giving off to the melt the major part of the silicon contained therein. The gas streaming upwardly from the surface of the melt is relatively lean so far as semiconductor material is concerned, and the possibility of separation on the solidified but as yet hot rod v body having a magnetic moment. induction coil surround the extended axis of `the crystal amounts of material of the ydrop 4 are .crystallized on the solid rod 3 which correspond yto the amounts separated 'from the reaction gas. The size of the molten drop and therewith the sizeof the crystallization plane remain accordingly constant. In order to adjust the speed of crystallization to the drawing speed,l cooling means may be tion o f the arrow 6, with a speed such that the upper por- `tion of the tiuid drop-is cooled,l off and solidities upon leaving the' induction eld of the coil 5.` The drawing speed provided for accelerating the speed a't which the material solidilies. However, in the case of silicon, this will not be necessary. ,The reaction vessel as well as the gas supply conduits may be suitably cooled so as to prevent excessive hea-ting thereof and therewith separation thereon of the semiconductor material.

The symmetry plane of the induction coil is .positioned somewhat below the molten drop. The drop is accordingly positioned within a range of the electromagnetic tield possessing a gradient which effects a force operating in a direction opposite to that ofthe force of gravity, thereby supporting the drop electromagnetcally. The dimensioning of the supporting force is a matter of experience and is increased by increasing the coil current. VIt is, however, advisable to elect the support of the drop independent of the heating source. This can be effected electromagnetically inthe following manner:

An induction coil which isv traversed by current produces in known manner a magnetic iield with thelines of force diverging at the ends upon leaving the coil. The magnetic iield accordingly posseses a noticeable lield gradient which effects a translating force with respect to a lf the windings of the member 3 circularly, with the coil windings `being disposed along planes extending approximately perpendicularly to the vertical axisof the crystal member, the gradient of the field at the upper end will be in the direction of the force of gravity, and the gradient at the lower end ofthe coil will be in a direction opposite to that of the vforce of gravity. The melt is due to the induction etect traversed by eddy currents, therefore having a magnetic moment the direction of which is, -in accordance with the Lenz rule, so oriented that the melt receives a force opposed to ythe lield gradient, and it will be clear, therefore, that a force will act on the molten drop which is opposed to the vforce of gravity when the drop is situated within the range of the upwardly diverging magnetic lines of force. This will be assuredly the case when the Windings of the induction Vcoil surround the crystal 3 concentrically and when the drop is situated somewhat above the coil. The heating coil acts in such a case also as a supporting coil.

However, it is also possible to provide below theheati by initially mounting Ain the yreaction vessel 1 a cylindrical tbody 3 of monocrystalline silicon, about 5 centimeters long and 20 millimeters thick, afterrst cleaning such 'body with -fluoric acid and drying it.. The silicon crystal body 3 may also be subjected to thorough cleaning by means of etching. The reaction vessel 1, thus provided Vwith the silicon crystal 3, is thereupon relieved of any residual moisture by conducting therethrough a stream of hydrogen. The induction coil 5 is thereafter placed in position so that its windings are situated concentrically about the extended axis of the lower end of the crystal 3 or better somewhat below Vthe lower end thereof. High frequency energy is then supplied tothe induction coil, the

strength of the coil current being increased until the lower end is melted to form the drop depending therefrom. The use'of preheating, for example, by means of an infrared beam (not shown), directed against the lower end of the crystal 3, which is to be melted, or the use, for this purpose, ofa radiation produced by another device, for example, illumination, willV contribute toward considerably accelerating the melting operation even in thecase of high ohmic semiconductor material.

The energy of thehigh frequency coil is 'increased from initially low values until the ylower end of the crystal 3 is molten to form the drop depending from a crystal part which remains in solid state. The size-.of the drop is' ascertained by experience and numerical values that would be valid for all' cases cannot be given. The drop shall however be of a size such that its prole forms with the profile of the solid crystal portion an angle as extended as possible or, as'will be better in many cases, for example, in the case of silicon, that the prole of the drop extends somewhat beyond the solid crystal. In the event that this is impossible owing to the surface tension of the molten material, the drop must be supported additionally. The melting is suitably elected in hydrogen gas.

The Ameling can be easily observed through a dark coloredk glass, since the molten Amaterial distinguishes optically from the solid material, and no difficulties will therefore be experienced in imparting to the drop a size such as indicated above. The appearance of instability is clearly recognized by a constriction starting to form with respect to the prole of the drop, and such condition can be counteracted and cancelled out by appropriate' regulation of the heating of the drop. The danger of the dropping olf of the molten drop can thus be easily prevented by careful work. The elect of supporting rneasures, for example, by electromagnetic support of the drop source which produces it adjusted so as to provide for substantially constant dropsize. The supply of the reaction gas is in FIG. 1 effected through the nozzle 2 which is disposed underneath the drop4, the purified reaction gas blowing against the drop in a uniform stream. The reaction gas decomposes at the hot surface of the drop, thereby separating pure silicon which is taken up by the drop, the leanspent gases moving upwardly for discharge. The amount of separated material grows with the growth of the drop surface and the drop temperature (which generally must not be considerably increased above the melting point of the material involved), and further with the amount of the silicon-containing compound in the reaction gas which contacts the drop in a time unit. The amount of the separation also depends upon the kind of the compound and can be calculated in accordance with known rules governing thermodynamics. Accordingly, the increase in the size of the drop, in a unit of'time,

effected by the separation of the material, can be easily determined by calculation.

However, it will generally sutlice to rely upon visual observation and to start withdrawing the solid crystal body as soon as the drop begins to grow noticeably due to the separation thereon of the silicon, thus also obtaining in simple manner based upon observation, the withdrawal speed and the progressive cooling connected therewith. The withdrawal speed is so adjusted that it is proportional to the speed of material separation or precipitation thereof, which is recognized by observing that the drop size remains constant during the progress of the separation. Fluctuations in the size of the drop are in simple manner equalized or compensated by constantly elfected increase or decrease of the drawing speed or by increase or decrease of the supply of reaction gas, respectively.

ln the example shown in FIG. t2, the melt is in the form of a liuid zone 4 which extends between two solid highly o pure silicon rods 3 and 3.

The melt may be produced, for example, by melting a median zone of a vertically positioned silicon rod. The molten'zone must be such as to completely separate the solid portions of the rod so that they can lbe'drawn apart to produce the benefits of thedownwardly depending molten drop. The reaction functioning merely as a mechanical support for the molten zone 4. Instead of rotating one or both parts of the rod, the molten zone 4 may be rotated, for example, by means of a rotating eld which permeates the molten zone. These and similar measures, for example, use ofY vibration for agitating the molten zone, can in some circumstances be advantageously applied.

FIG. 2 also shows means for producing an electric blast directed against the melt. The melt 4 is for this purpose connected, over one of the crystal members, in the illustrated case over the crystal member 3', with one terminal of an appropriate high voltage direct current source 14, such source being alsoconnected to electrodes such as 1S, 15', each of which is provided with a pointed end facing in the direction ofthe melt.

In the embodiment illustrated in FIG. 3, the melt 4 is produced by a gas discharge extending from the lower end of the crystal body 3 to a hollow cooled counter electrode 16, the gas discharge being effected by a voltage source 17. As a result of the cooling of the hollow coun- 'ter electrode, for example, by means of a cooling gas or liquid owing therethrough, the temperature at the surface of the electrode will not exceed the decomposition temperature of the reaction gas, and a noticeable separation or precipitation of semi-conductor material will not be affected on such electrode. This result is also obtained if the counter electrode is circuited as anode and the crystal body as cathode of a 'direct current discharge. Suitable cooling can also be applied to other parts of the apparatus at which separation or precipitation of semiconductor material is not desired.

The invention may obviously be employed not only in the production of silicon or germanium semiconductor elements but can also be successfully applied in the production of mixed semiconductor bodies consisting of elements of the third and fifth groups of the periodic system of elements. It is of course necessary that the reaction gas contains, in the required proportions, the components of the semiconductor to be produced, which are to be given off from the gas phase at the surface ofa melt whichV depends in the fashion of a drop from a solid crystal body made of the corresponding mixed semiconductor material. Doping substances can likewise be employed-to affect the melt foribuilding into the semiconductor rod in accordance with a desired scheme, for ,the purpose of producing homogeneously doped semiconductor rods and also rods with zones of different conduction type. The solid crystal bodies may also consist of a crystalline material which serves in known manner for determining a monocrystalline structure in the material whichvis being solidified from the molten drop.

. Changes may be made within the scope andspirit of the appended claims which dene whatis believed to be new and desired to have protected by Letters Patent.

We claimi l l. A method of producing rod-shaped semiconductor crystals, comprising the steps of disposing in a suitable reaction vessela solid rod-shaped body made 'of the semiconductor substance which is to be produced vso as to extend vertically therein, applying an energy source to effect melting a portion of said rod so as to form at the lower end thereof a melt which depends downwardly therefrom in the manner of a drop, conducting to said melt a reaction gas which contains components of the semiconductor substance to be produced so as to effect decomposition of said gas and consequently separation. therefrom of said semiconductor substance, said separated semiconductor substance precipitating on said melt, and moving said rod upwardly at a speed adjusted to the rate of precipitation of semiconductor substance on said melt, whereby the solided portion of the rod, on which material from the melt crystallizes to effect growth of the rod, is removed from the range of action of the energy source to maintain the size of said melt substantially constant.

2. A method according to claim 1, comprising supporting said melt pneumatically.

3. A method according to claim l, comprising supporting said melt by the action of an electromagnetic field.

4. A method according to claim l, comprising transporting to said melt semiconductor particles produced in the free gas space by the application of an electric blast.

5. A method according to claim l, comprising pre'- heating the portion of said semiconductor rod which-is to form the melt by high frequency induction.

6. A method according to claim l, wherein said energy sourceis a gas discharge. o

7. A method according to claim l, comprising supporting said melt by the action of a further solid rodshaped semiconductor body extending downwardly therefrom.

References Cited by the Examiner UNITED STATES PATENTS .2,692,839 10/1954 Christensen et al. 14S- 1.5 2,907,642 10/1959 Rummel 1481.6x 2,964,396 12/1960 Rummel et al. 75-10 2,993,762 '//1961 sterling et a1 14s- Lax 3,098,741 7/1963 Enk et a1. 75-10 FOREIGN PATENTS 525,102 1/1954 Belgium. S 42,2941 9/1956 Germany.

OTHER REFERENCES Keck et al.: Review of Sci. Instr., vol. 25, No. 3, March 1954, pp. 298, 299. DAVID L. ECK, Primary Examiner.

MAURICE A. BRINDISI, WINSTON A. DOUGLAS,

' Examiners. 

1. A METHOD OF PRODUCTING ROD-SHAPED SEMICONDUCTOR CRYSTALS, COMPRISING THE STEPS OF DISPOSING IN A SUITABLE REACTION VESSEL A SOLID ROD-SHAPED BODY MADE OF THE SEMICONDUCTOR SUBSTANCE WHICH IS TO BE PRODUCED SO AS TO EXTEND VERTICALLY THEREIN, APPLYING AN ENERGY SOURCE TO EFFECT MELTING A PORTION OF SAID ROD SO AS TO FORM AT THE LOWER END THEREOF A MELT WHICH DEPENDS DOWNWARDLY THEREFROM IN THE MANNER OF A DROP, CONDUCTING TO SAID MELT A REACTION GAS WHICH CONTAINS COMPONENTS OF THE SEMICONDUCTOR SUBSTANCE TO BE PRODUCED SO AS TO EFFECT DECOMPOSITION OF SAID GAS AND CONSEQUENTLY SEPARATION THEREFROM OF SAID SEMICONDUCTOR SUBSTANCE, SAID SEPARATED SEMICONDUCTOR SUBSTANCE PRECIPITATING ON SAID MELT, AND MOVING SAID ROD UPWARDLY AT A SPEED ADJUSTED TO THE 